1. Field of the Invention
This invention pertains to the field of fracturing subterranean formations penetrated by a well bore. More particularly, this invention pertains to the fracturing of subterranean formations using an aqueous crosslinked gelled fracturing fluid containing certain cationic polymers which improves the overall effectiveness of the fracturing process.
2. Prior Art
Hydraulic fracturing is a well known process, as illustrated by the text "Hydraulic Fracturing" by G. C. Howard and C. R. Fast, Monograph Volume 2, Henry L. Doherty Series, Society of Petroleum Engineers of AIME, Dallas, Tex. (1970). This book provides an excellent, but somewhat dated, introduction into the field of hydraulic fracturing.
In a hydraulic fracture, an aqueous hydraulic fracturing fluid is injected through a wellbore against a formation at flow rates and pressures such that a fracture in the formation is initiated and/or extended. The hydraulic fracturing fluids are normally aqueous based fluids containing a polymeric gelling agent and a proppant (e.g. 20/40 mesh sand or bauxite). The gelled aqueous hydraulic fracturing fluids can be crosslinked or uncrosslinked. Most hydraulic fracturing fluids used today are aqueous solutions of guar or hydroxypropylguar crosslinked by borate anions or by certain polyvalent metal cations. The crosslinked fluids have better proppant-carrying capacity as well as better physical and chemical strength to withstand the rigors of temperature, pressure and shear imposed upon a fracturing fluid.
The purpose of hydraulic fracturing is, of course, to stimulate the production of subterranean fluids from the formation by providing permeable channels into the formation. Hydraulic fracturing has been used to stimulate the flow of water, oil and/or gas. This purpose can be defeated or the efficiency of the fracture diminished by the swelling of water-sensitive clays and/or the migration of clay fines and other minute particles in the formation. The problems associated with clays and/or fines in the treatment of wells is shown by the following (non-inclusive) listing of journal articles and patents: (1) SPE 4785 Hower (1974); (2) SPE 4786 Barkman et al. (1974); (3) SPE 5692 Haskin (1976); (4) SPE 6008 McLaughlin et al. (1976); (5) SPE 6009 Reed (1976); (6) SPE 6129 Stout et al. (1976); (7) SPE 6759 Copeland et al. (1977); SPE 7007 Muecke (1978); (8) SPE 7566 Thomas et al. ( 1978); (9) SPE 8795 Davies (1980); (10) SPE 8797 Williams et al. (1980); John E. Moore, The Petroleum Engineer, B-40 (February 1960); Carl D. Veley, Journal of Petroleum Technology, 1111 (September, 1969); H. C. McLaughlin et al., World Oil, 58 May 1977); John K. Borchardt et al., Paper No. 79-30-12 presented at the May meeting of the Petroleum Society of CIM (May 1979); Walter Rose, SPE-AIME Symposium (August, 1979).
Reference is also made to the following U.S. patents:
______________________________________ 3,108,069 3,382,924 3,349,032 3,537,524 3,603,399 3,610,338 3,654,164 3,738,425 4,031,959 ______________________________________
The above articles and patents generally set for the background and illustrate the problem associated with clays and fines in the treatment of wells.
Quaternary ammonium compounds have been used extensively to stabilize clays and prevent migration of fines. The quaternary ammonium compounds have been monomeric (e.g. ammonium chloride) or polymeric (e.g. U.S. Pat. No. 4,158,521 and German Offenlegungsschrift 27 36 277 (reference U.S. patent application Ser. No. 714,213 filed Aug. 13, 1976; and see U.S. patent application Ser. No. 901,664 filed May 4, 1978 both entitled "Oil Well Treating Method and Composition" by Homer C. McLaughlin et al.)). U.S. Pat. No. 4,158,521 teaches the use of the reaction product of dimethylamine and epichlorohydrin. The German Offen. teaches that a variety of polymeric quaternary ammonium or phosphonium compounds as well as a variety of polymeric sulfonium compounds can be used. The closest compounds to the present invention in the German Offen. is a methacrylate polymer having pendant ammonium groups separated from the ester oxygen by three carbon atoms. The German Offen. mentions fracturing only in the most casual sense.